Referring to FIG. 1, a plasma processing system may include a high or radio frequency (hereinafter referred to as ‘RF’) matching network 100, a variable impedance load (e.g. a plasma processing chamber) 102, an RF generator 104, and an RF delivery system 106. The RF matching network 100 is disposed between and electrically coupled to the RF delivery system 106 and the variable impedance load 102. The RF delivery system 106 is electrically coupled to the RF generator 104. The RF matching network 100 may include electrical components of known or variable impedance values (e.g., variable capacitors and/or inductors). The RF delivery system 106 may include items such as a high power coaxial cable assembly and connectors.
The RF generator 104 may provide RF energy to the variable impedance load 102 via the RF delivery system 106 and the RF matching network 100. The function of the RF matching network 100 may be to match the impedance of the variable impedance load 102 to the output impedance of the RF generator 104 and RF delivery system 106. By matching the impedance of the variable impedance load 102 to the output impedance of the RF generator 104 and the RF delivery system 106, the reflection of the RF energy from the variable impedance load 102 may be reduced. Reducing the reflection of RF energy may effectively increase the amount of RF energy provided to the variable impedance load 102 by the RF generator 104.
A first technique of RF matching may include varying the electrical impedance of the capacitors and/or inductors until the impedance of the variable impedance load matches the output impedance of the RF generator. FIG. 2 is a more detailed schematic drawing depicting the prior art RF matching network 100. The depiction shows the asymmetrical arrangements of a tune component 108 and a load component 110 of the RF matching network 100. In addition, RF matching networks 100 are typically asymmetrical in the arrangement of the tune 108 and load components 110.
A second technique of matching the impedance of the variable impedance load 102 to the impedance of the RF generator 104 may utilize variable frequency matching. The impedance presented by the RF matching network 100 to the output of the variable RF frequency generator 104 may change with the frequency. By outputting a particular frequency from the RF generator 104, the variable impedance load 102 may match the impedance of the RF generator 104 and the RF delivery system 106. This technique may be referred to as variable frequency matching. Variable frequency matching may employ the RF matching network 100 that includes fixed value tune components 108 and load components 110 (e.g. fixed value capacitors, inductors and/or resistors). The values of the tune components 108 and load components 110 may be selected to help ensure that the impedance of the RF generator 104 will match the impedance of the variable impedance load 102.
Prior art RF matching networks may help reduce the amount of energy reflected by the variable impedance load. However, the inventors of the present invention have determined that in some circumstances, existing RF matching networks may not reduce the amount of reflected energy sufficiently to avoid problems. Thus, what is needed are improved methods and apparatus for RF matching.